Multielement radio-frequency antenna structure having linearly arranged elements



Nov. 17, 1970 Filed Sept. 25, 1967 R. J. FRANCIS ETAL 3,541,567 MULTIELEMENT RADIO-FREQUENCY ANTENNA STRUCTURE HAVING LINEARLY ARRANGED ELEMENTS 3 Shoots-Sheet 1 INVENTORS RICHARD J. FRANCIS 8 CLARA A. FRANCIS MAHONEY, MILLER 8 RAMBO ATTORNEYS NOV. 17 1970 J, N IS ETAL 3,541,567

- 'MULTI'ELEMENT RADIO-FREQUENCY ANTENNA STRUCTURE HAVING LINEARLY ARRANGED ELEMENTS Filed Sept. 25, 1967 3 Sheets-Sheet 2 FREQUENCY 0: INVENTORS RICHARD J. FRANCIS 8 CLARA A. FRANCIS FREQUENCY MAHONEY, MILLER 8 RAMBO BY W ' ATTORNEYS NOV. 17, 1970 R, J FRANCls ETAL 3,541,567

MULTIELEMENT RADIO-FREQUENCY ANTENNA STRUCTURE HAVING LINEARLY ARRANGED ELEMENTS Filfid Sept. 25, 1967 3 SheetS-Sheet 5 INVENTORS RICHARD J. FRANCIS BY CLARA A. FRANCIS MAHONEY. MILLER & RA BO BY A/ M- TTORNEYS United States Patent MULTIELEMENT RADIO-FREQUENCY ANTENNA STRUCTURE HAVING LINEARLY ARRANGED ELEMENTS Richard I. Francis and Clara A. Francis, both of 11855 Broad St., Pataskala, Ohio 43062 Filed Sept. 25, 1967, Ser. No. 670,153 Int. Cl. H01q 1/40 US. Cl. 343-873 Claims ABSTRACT OF THE DISCLOSURE DETAILED DESCRIPTION The antenna structure of this invention is primarily adapted to mobile transmitter-receiver installations such as would be utilized for citizens-band operations in connection with automotive vehicles although the antenna structure is adaptable to other frequency-band allocations. In the usual installations of this type, the antenna is a single element, electrically conductive element effective as both a receiver and radiator of electromagnetic wave energy and is of a construction to resist the forces that may be applied as a consequence of vehicular movement.

The most common mobile antennas are an electrical quarter wave in length and metallic. They range in length from about 9 feet for 27 megacycles to about 6 inches for 470 megacycles. They are vertically mounted and supported only at the bottom. They are end-fed.

Vertical quarter wave antennas are physically unwieldy when more than 9 feet long. However, any electrical quarter wave antenna in the 1 to 500 megacycle range may be physically shortened by adding inductance in series. Conversely, the physical length, commonly called aperture, is increased by adding capacitance in series.

Quarter wave antennas are desirable because when endfed they approach resonance. Resonance is a state where inductance and capacitance reactances are equal and as a result the total impedance is its direct current resistance.

In a two-way radio communications the transceiver and antenna are connected with coaxial cable, and the most commonly used coaxial cable has a characteristic impedance of 52 ohms. The output stage of the transceiver is adjustable to 52 ohms. However, the terminal impedance of an end-fed quarter Wave is Well below 52 ohms, perhaps as low as ohms.

Maximum power transmission results when the terminal impedance of the end-fed quarter wave antenna matches the impedance of the coaxial transmission line. With the single element antennas of prior art the impedance mismatch is great enough to seriously impede the efficiency of power transferral. Some installations are operated inefliciently with this mismatch, while other installations rely on complex impedance matching networks to correct this mismatch.

The antenna structures of this invention may be readily adapted for use throughout the frequency spectrum of 1 to 500 megacycles.

3,541,567 Patented Nov. 17, 1970 It is, therefore, an important object of this invention to provide a novel antenna structure which may be con structed to provide a more advantageous impedance match with that of a connecting coaxial transmission cable.

It is another important object of this invention to pro vide a novel antenna structure for mobile, vehicular installations that comprises a multiplicity of electrically conductive elements encased in a structurally supporting body of synthetic resin capable of withstanding the structural load forces that may be imposed in a mobile, vehicular installation.

It is another object of this invention to provide an antenna structure having a multiplicity of elongated, electrically conductive elements grouped in parallel relationship and having a desired characteristic impedance for a particular design.

It is a further object of this invention to provide an antenna structure for a particular design frequency band and having a multiplicity of electrically conductive elements of different diameters to provide a relatively wide bandwidth while maintaining a relatively high response and radiation characteristic for the entire frequency band.

It is also an object of this invention to provide an antenna structure for a particular design frequency band and having a multiplicity of electrically conductive elements of different lengths to provide a wide bandwidth while maintaining a relative high response and radiation characteristic for the entire band.

*It is also an object of this invention to provide a novel antenna structure which may be economically fabricated.

These and other objects and advantages of this invention will be readily apparent from the following detailed description of embodiments thereof and the accompanying drawings.

In the drawings:

FIG. 1 is a medial, longitudinal sectional view of an antenna structure embodying this invention.

FIG. 2 is a transverse sectional view taken along line 2-2 of FIG. 1.

FIG. 3 is a transverse sectional view similar to FIG. 2 of an antenna structure of modified construction.

FIGS. 4 and 5 are graphic representations of the frequency response characteristic of electrically conductive elements to electromagnetic wave energy.

FIG. 6 shows an elf-center placement of the conductors.

FIG. 7 is a medial, longitudinal sectional view of a modified form of an antenna structure embodying this invention.

FIG. 8 is a transverse sectional view taken along line 88 of FIG. 7.

An antenna structure designed for either transmission or reception of radio-frequency, electromagnetic radiation and embodying this invention is illustrated in detail in FIGS. 1 and 2 of the drawings. This antenna structure is designed in particular for mobile, vehicular installations where the antenna is vertically disposed and attached to the vehicle by suitable mounting hardware (not shown). Forming the electrical elements of this antenna structure are a multiplicity of elongated electrical conductors, three in this embodiment 10, 11 and 12, which are supported in a generally vertically disposed, parallel relationship. Each conductor may be formed from a length of circular cross section copper wire with the several conductors not being self-supporting in the desired configuration due to the physical dimensions of the conductors.

A supporting body 13 for the conductors 10, 11 and 12 is formed by a solidified matrix of synthetic resin which has suitable characteristics as to flexural strength and modulus for the specific design application. The several electrical conductors are centrally embedded in the resin matrix which is capable of withstanding the static and dynamic loads that may be imposed in such vehicular installations and maintain the relative parallel configuration of the conductors. Preferably, the resin matrix, which may consist of a thermosetting polyester or epoxy, also includes strands of fiber glass 15 distributed throughout the body to enhance the mechanical properties of the antenna structure. These strands may be oriented longitudinally and some strands may be oriented helically in the surface.

The electrical conductors 10, 11 and 12 are electrically insulated from each other throughout their length to prevent electric current conduction as between any two conductors. Effective electrical insulation of the conductors 10, 11 and 12, when grouped as illustrated in FIG. 2 in a triangular configuration, may be accomplished by sheathing at least two of the conductors with a dielectric material throughout their length. In the embodiment illustrated in FIGS. 1 and 2, two conductors and 11 are shown with a respective dielectric sheath 16 or 17 applied which effectively insulates the three conductors from each other. This dielectric sheathing may comprise a coat of varnish; however, other well known material may also be utilized which does not provide electromagnetic shieldings. If desired, the dielectric sheath may be omitted as to all conductors and spacing of the conductors to provide electrical insulation achieved by other means. Also, all conductors may be provided with a dielectric sheath.

In completing the electrical circuit connections of this antenna structure, the conductors 10, 11 and 12 are electrically interconnected at one end as is illustrated in FIG. 1. This may be mechanically accomplished by soldering portions of the exposed conductive elements together and to a mounting ferrule 14. The opposite ends of the conductors are not electrically connected and the electrical circuit thus presented comprises a group of parallel conductors which are open circuited at one end and will prevent current circulation within the two conductors.

Through selection of conductors 10, 11 and 12 of appropriate cross-sectional area and through proper spacing of the elements, an antenna structure may be constructed having a predetermined value characterstic impedance. This impedance is determined by physical spacing and cross-sectional area of the conductors and is substantially independent of frequency of the electromagnetic wave energy or physical linear length of antenna.

In the usual mobile installation, the desired characteristic impedance for proper matching is 529 as this is the impedance of the most commonly used commercially available coaxial transmission cable.

As in the case of conventional antennas, the antenna structure of this invention will preferably be a quarter wave length for the specific design frequency band.

One of the parameters controlling the physical length of an end-fed electrical quarter wave antenna is the diameter of the conductor. For a given electrical quarter wave the physical length of the conductor decreases as the conductor diameter increases, but not as a straight line function. FIG. 4 illustrates this condition. Curve M shows the response of a conductor of a given diameter, while curve N is the response of a conductor of another diameter. FIG. 4 shows that their resonant frequencies are at different frequency values in the spectrum, and illustrates how a multiplicity of conductors of dissimilar diameters broadens the effective bandwidth of an antenna.

FIG. 5 illustrates how conductors of different physical lengths have their maximum response at dissimilar frequencies when end-fed as quarter wave antenna. Curves P and S represent conductors of different physical lengths, and their resonant frequencies may be widely displaced.

A metallic mounting ferrule 14 is provided to facilitate attachment of the end-fed quarter wave antenna to the vehicle. This ferrule 14 is formed with a central socket in which an end of the antenna structure is inserted and secured as by a suitable adhesive or bonding material. The ends of the conductors 10, 11 and 12 which are exposed extend through an aperture 18 and may be soldered to the ferrule 14 as at 19.

Although the illustrated embodiment comprises three conductors 10, 11 and 12, the number of conductors may be increased. For example, five such conductors, 20, 21, 22, 23, and 24, as shown in FIG. 3, may be formed into a similar antenna structure to obtain the desired characteristic impedance with the desired frequency band response. Construction may be facilitated by providing a central core 25 which may also be made of the same type resin and fiber glass strands and encased in a resin and fiber glass sheath 26.

In FIG. 6 we show the conductive elements 10a, 11a, and 12a off-center rather than concentric as in FIG. 2.

A cylindrical dowel of this structure can be taper ground to exposed ends of conductive elements in the surface of the taper. This taper grinding results in conductive elements of different lengths and an antenna structure having a broader frequency response. An antenna structure of such modified form is more clearly illustrated in FIGS. 7 and 8 where the three conductive elements 26, 27 and 28 are disposed in a single plane and embedded in a solidified matrix of synthetic resin including distributed strands of fiber glass in accordance with the previously described construction of an antenna body 29. One end of the body 29 is secured in a mounting ferrule 30 with exposed terminal end portions of the three conductive elements 26, 27 and 28 mechanically secured to the ferrule to form a suitable electrical connection. The elements are shown relatively spaced apart to obtain the necessary electrical insulation with the spacing exaggerated for clarity in illustrating the different length of conductive elements that are obtained through a taper grinding process.

It will be readily apparent that a novel antenna structure is provided which may be readily constructed with the desired characteristic impedance. Utilizing conductors of different diameters and lengths provides a broadband frequency response.

According to the provisions of the patent statutes, the principles of this invention have been explained and have been illustrated and described in what is now considered to represent the best embodiment. However, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

Having thus described this invention, what is claimed 1. A radio-frequency antenna structure comprising at least three elongated, electrically conductive elements for directly radiating and receiving electromagnetic wave energy, each of said elements being electrically insulated from and separated from the other throughout their length by only dielectric material but being interconnected at the same one end to form a direct electrical connection, said elements being of selected cross-sectional area and disposed in linearly extending, spaced parallel relationship to provide a desired characteristic impedance, and a body structure formed from a dielectric material in which said electrically conductive elements are embedded for support thereof in relatively fixed relationship, said dielectric material having a relatively low loss characteristic as to electromagnetic wave energy and physical strength characteristics to maintain the physical configuration of the conductive elements and assure structural integrity of the antenna structure.

2. An R-F antenna structure according to claim 1 wherein said three elements are disposed in a triangular configuration.

3. An R-F antenna structure according to claim I having a multiplicity of electrically conductive elements, said elements disposed in a circular configuration.

4. An R-F antenna structure according to claim 1 wherein said supporting structure is a fiber glass-reinforced, synthetic resin in which said electrically conductive elements are encased, said structure including a multiplicity of longitudinally extending strands of fiber glass.

5. An R-F antenna structure according to claim -4 wherein said synthetic resin is a thermosetting polyester.

6. An R-F antenna structure according to claim 4 wherein said synthetic resin is an epoxy.

7. An R-F antenna structure according to claim 4 in which said fiber glass strands are distributed through the core and shell of said resin matrix.

8. An R-F antenna structure according to claim 1 where the elongated electrically conductive elements extend for different lengths.

9. A radio-frequency antenna structure comprising at least three elongated, electrically conductive elements for directly radiating and receiving electromagnetic wave energy, each of said elements being electrically insulated from the other throughout the length thereof but being electrically connected together at only one end thereof, said elements being of selected dissimilar cross-sectional area to provide a relatively greater effective bandwidth at the nominal operating frequency and relatively spaced to provide a desired characteristic impedance, said electrically conductive elements arranged in linearly extending relationship and a supporting body structure for said electrically conductive elements formed from a dielectric having a relatively low loss characteristic as to electromagnetic wave energy and physical strength characteristics to maintain the physical configuration of the conductive elements and assure structural integrity of the antenna structure.

10. A radio-frequency antenna structure comprising at least three elongated, electrically conductive elements for directly radiating and receiving electromagnetic wave energy, each of said elements being electrically insulated from the other throughout the length thereof but being electrically connected together at only one end thereof, said elements being of selected cross-sectional area and relatively spaced to provide a desired characteristic impedance, said electrically conductive elements arranged in linearly extending relationship and a supporting body structure for said electrically conductive elements formed from a dielectric having a relatively low loss characteristic as to electromagnetic wave energy and physical strength characteristics to maintain the physical configuration of the conductive elements and assure structural integrity of the antenna structure, said body structure being tapered along its length and reducing in diameter from the end at which said conductive elements are connected together with each of said conductive elements terminating in the surface at a respectively different point along its length.

References Cited UNITED STATES PATENTS 2,681,412 6/1954 Webster 343-873 3,077,569 2/1963 Ikrath 343-785 X 3,155,975 11/1964 Chatelain 343-873 X 3,268,896 8/1966 Spitz 343-785 X HERMAN KARL SAALBACH, Primary Examiner S. CHATMO'N, JR., Assistant Examiner US. Cl. X.R. 343-783 

